The invention is concerned with ocular diagnostics, and more particularly it relates to an improved system for profilometry of the cornea by detecting the apparent location of point sources of light as reflected paraxially from the cornea. The invention encompasses the profilometry system and also a subsystem which provides an array of point light sources to enable profiling of the cornea over a wide area.
U.S. Pat. No. 5,054,907 disclosed a system for detecting the shape of the central portion of the cornea, including that region immediately around the optical axis (e.g. the central 2 mm.). That patent is incorporated herein by reference. The technique and system disclosed in the patent involved forming virtual point light sources inside the objective lens of a diagnostic system, or between the objective lens and the patient. The virtual point light sources were real images of point light sources. This brought an array of point light sources directly adjacent to the optical axis (the array may extend across the optical axis), thus enabling the profilometry of a central region of the cornea which was difficult to profile with previous equipment involving light sources strictly peripheral to the objective lens.
The patented system included use of the objective lens as a field lens for the paraxially reflected pattern image, in order to expand the region of coverage on the cornea. However, profiling widely enough to include outer regions of the cornea along with the central region would still be a problem unless a very "fast" objective lens (i.e. having high numerical aperture) were used, which may need to be objectionably large or positioned objectionably close to the eye.
An example of a previous perimeter device with peripheral light sources is shown in Wilms Patent No. 4,312,574. None of the perimeter devices was capable of efficiently providing point light sources useful to image all important regions of the cornea, including near the optical axis.
Achatz et al. Patent No. 4,159,867 is also somewhat pertinent to this invention. However, the apparatus shown in that patent used a different set of reflected rays, and also used, in a preferred embodiment, a cardoid-shaped surface. In addition, the disclosed device did not project a set of target spots through the refractive optics, which comprised a visual telescope rather than a system for delivery/collection of treatment, ranging, tracking or viewing channels. The system preferably used as small a telescope as possible, located in the plane of the cardoids, and the patent indicated it was preferred not to use a video camera for detection of the reflected rays.
A combination of peripheral, external point light sources with the patented system just described was disclosed in copending application Ser. No. 656,722, now U.S. Pat. No. 5,170,193, referenced above. The present invention includes variations and improvements on the system disclosed in the copending application.